Introduce a step-by-step git commiter

[sledigabel]

On large repo lists, one often has to run this kind of workflow:

turbolift clone
turbolift forearch <insert here the command to change the repo>

then, to validate the changes, they would run something like this:

turbolift foreach git diff
<frantically scroll through thousands of lines to figure out whether all repositories are successfully changed>
<then, trusting your eye sight, you stage and commit>
turbolift commit

It would be nice to have a way to commit those step-by-step with a visual validation from the user, introducing a --incremental.

The workflow would look like:

turbolift commit -i
-- Repository: REPOSITORY_NAME_1
<git diff on this specific repo>
<prompt for the user to confirm with a y/N>
-- Repository: REPOSITORY_NAME_2
...

We will log in the end the repo list that WASN'T updated, the user can decide what to do with it then.